The present invention relates to seals, and more particularly pertains to a unitized radial and facial seal intended principally for use between radially inner and outer relatively rotationally and axially movable members.
There are numerous applications in which relatively rotating members require a seal or seals to retain lubricant and exclude contaminants. Sealing a shaft in a contaminated environment while the shaft is simultaneously rotating and undergoing axial reciprocation presents a very difficult sealing problem. Conventional rotary shaft seal designs include lips intended to run on a very thin surface lubricant film on a rotating shaft. Failure or absence of the lubricant film results in high friction and attendant rapid wear of the sealing lip. Accordingly, in a rotating application, the force used to bias the sealing lip against the shaft should not therefore be so great as to cause the seal lip to break through the lubricant barrier which "wets" or adheres to the shaft surface. Due to the relatively low seal-to-shaft bias force, a seal designed to operate in a rotary application will fail in an axial reciprocating application because lubricating oil will bypass the sealing lip as the shaft moves axially. When the shaft moves to an axially extended position, contaminants will collect on the surface of the shaft. Subsequently axial retraction of the shaft tends to force the collected contaminants into the seal lip. The very fine and typically abrasive contaminant particles will pass under the seal lip because the seal-to-shaft bias force is not sufficient to break through the lubricant film. The contaminant particles will abrade both the sealing lip and the shaft and over time the shaft will become scored, resulting in lubricant leakage.
Conversely, a seal designed to operate in a reciprocating application, in the absence of rotation, relies upon a sufficient force being exerted upon the sealing lip to cause the lip to break through the lubricating film and run directly against the mating surface. Seals of this design are referred to as "wipers" because their function is to wipe lubricant from the shaft as the shaft moves from a retracted position to an extended position and to wipe contaminants from the shaft as it moves from an extended position back to a retracted position. A wiper seal will tend to wear out very quickly in a rotary application because it breaks through the lubricant film which adheres to the mating surface.
It is therefore desirable to isolate radial and facial seals so that they are only required to seal dynamically with respect to one plane or surface. For example, any radial seal that must seal against a rotating counterface should not also be subjected to a reciprocating motion of that counterface; and any facial seal that seals against a counterface that is reciprocating axially should not be exposed to rotational movement of that counterface.